Vagrant: Ensure IP Subnet not in use by localhost (#12332)

* feat(subnet): Ensure Vagrant subnet not in use by localhost

This commit ensures that Vagrantfile supplied $subnet is not in use by
the localhost. Previously, if the subnet is in use by localhost (i.e.
bridge network), Vagrant VM boxes can not communicate.

* refactor(socket): Use ruby Socket library to find addrs

This commit reverts the usage of Ruby .scan() which may result in
failure if program is not provided. Instead, this commit refactors to
use Socket library to determine interfaces in use, then proceeds to
compare with Vagrantfile supplied subnets. Additionally, the commit
supports IPv6 comparisons.

Vagrantfile

@@ -4,6 +4,8 @@
 # For help on using kubespray with vagrant, check out docs/developers/vagrant.md
 
 require 'fileutils'
+require 'ipaddr'
+require 'socket'
 
 Vagrant.require_version ">= 2.0.0"
 
@@ -99,6 +101,33 @@ $extra_vars ||= {}
 
 host_vars = {}
 
+def collect_networks(subnet, subnet_ipv6)
+  Socket.getifaddrs.filter_map do |iface|
+    next unless iface&.netmask&.ip_address && iface.addr
+
+    is_ipv6 = iface.addr.ipv6?
+    ip      = IPAddr.new(iface.addr.ip_address.split('%').first)
+    ip_test = is_ipv6 ? IPAddr.new("#{subnet_ipv6}::0") : IPAddr.new("#{subnet}.0")
+
+    prefix  = IPAddr.new(iface.netmask.ip_address).to_i.to_s(2).count('1')
+    network = ip.mask(prefix)
+
+    [IPAddr.new("#{network}/#{prefix}"), ip_test]
+  end
+end
+
+def subnet_in_use?(network_ips)
+  network_ips.any? { |net, test_ip| net.include?(test_ip) && test_ip != net }
+end
+
+network_ips = collect_networks($subnet, $subnet_ipv6)
+
+if subnet_in_use?(network_ips)
+  puts "Invalid subnet provided, subnet is already in use: #{$subnet}.0"
+  puts "Subnets in use: #{network_ips.inspect}"
+  exit 1
+end
+
 # throw error if os is not supported
 if ! SUPPORTED_OS.key?($os)
   puts "Unsupported OS: #{$os}"